Laser crystallization of thin films on various substrates at low temperatures

ABSTRACT

A method and system are provided for crystallizing thin films with a laser system. The method includes obtaining a thin film comprising a substrate and a target layer that contains nano-scale particles and is deposited on the substrate. The heat conduction between the target layer and the substrate of the thin film is determined based on thermal input from the laser system to identify operating parameters for the laser system that cause crystallization of the nano-scale particles of the target layer in an environment at near room temperature with the substrate remaining at a temperature below the temperature of the target layer. The laser system is then operated with the determined operating parameters to generate a laser beam that is transmitted along an optical path to impinge the target layer. The laser beam is pulsed to create a localized rapid heating and cooling of the target layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional patent application of co-pending U.S.patent application Ser. No. 13/683,898 filed Nov. 21, 2012, whichclaimed the benefit of U.S. Provisional Application No. 61/562,458,filed Nov. 22, 2011 and U.S. Provisional Application No. 61/587,971,filed Jan. 18, 2012, and which is a continuation-in-part patentapplication of prior co-pending U.S. patent application Ser. No.13/113,386, filed May 23, 2011 (now U.S. Pat. No. 8,349,713), whichclaimed the benefit of U.S. Provisional Application No. 61/347,538,filed May 24, 2010. The contents of these prior applications areincorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention generally relates to methods of inducingcrystallization in thin films. More particularly, this invention relatesto methods of inducing crystallization in thin films at low temperatureswithout causing undue damage to a substrate of the thin film.

Many thin film applications require a limited amount of defects withinthe thin films such as grain boundary and point defects. For example,the conversion efficiency of thin film solar cells depends on thecrystallinity of photovoltaic (PV) materials (e.g., cadmium telluride(CdTE), copper indium selenide (CIS) and copper indium gallium selenide(CIGS)) that form the light absorbent layers of solar cells. Defects inthe photovoltaics degrade the photon-electron conversion efficiency andtransportation of electrons.

Traditional crystallization techniques used in the thin film industry,such as Rapid Thermal Annealing (RTA) techniques, have severallimitations. These limitations can include issues regardingnon-selective heating, slow crystal growth, temperature control forlarge crystal growth, and the need to use costly vacuum/inert gasenvironments. In particular, traditional crystallization techniques areperformed in environments at between 200° C. and 600° C. Thin films aregenerally formed of one or more layers that are deposited on a substratestructure. Therefore, these processes are not suitable for thin filmsthat are formed on a substrate with a melting temperature below theseoperational temperatures, for example, polymers.

In view of the above, it can be appreciated that there is a need forcrystallization techniques that overcome one or more of theselimitations, for example by being faster, more selective or lower cost.In particular, there is a need for crystallization techniques thatoperate at low temperatures without damaging a substrate of the thinfilms.

BRIEF DESCRIPTION OF THE INVENTION

The present invention provides a method and system suitable for inducingcrystallization in thin films at low temperatures without damaging thesubstrate of the thin film.

According to a first aspect of the invention, a method is provided forinducing crystallization in thin films with a laser system. The methodincludes obtaining a thin film comprising a substrate and a target layerthat contains nano-scale particles and is deposited on the substrate.The heat conduction between the target layer and the substrate of thethin film is determined based on thermal input from the laser system toidentify operating parameters for the laser system that causecrystallization of the nano-scale particles of the target layer in anenvironment at near room temperature with the substrate remaining at atemperature below the temperature of the target layer. The laser systemis then operated with the determined operating parameters to generate alaser beam that is transmitted along an optical path to impinge thetarget layer of the thin film and crystallize the target later. Thelaser beam is pulsed to create a localized rapid heating and cooling ofthe target layer.

According to a second aspect of the invention, a system is provided forinducing crystallization in a thin film that comprises a substrate andat least one target layer. The system includes a laser generating apulsing laser beam along an optical path to impinge the target layer ofthe thin film wherein the laser beam creates a localized rapid heatingand cooling of the target layer with the substrate remaining at atemperature below the temperature of the target layer.

A technical effect of the invention is the ability to inducecrystallization in thin films at room temperature. In particular, it isbelieved that, by pulsing the laser according to predetermined operatingparameters, a target layer within the thin film can be crystallizedwithout undue damage to a substrate of the thin film.

Other aspects and advantages of this invention will be betterappreciated from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically represents an exemplary embodiment of a lasersystem in accordance with an aspect of this invention.

FIG. 2 is a cross-sectional view schematically representing thecrystallization process within a thin film in accordance with an aspectof this invention.

FIG. 3 is a diagram representing steps for predicting optimum operatingparameters of the laser system of FIG. 1 in accordance with an aspect ofthis invention.

FIGS. 4(a) through 4(f) are scanned images showing surfaces of thinfilms after deposition on various substrates and the same surfaces aftercrystallization in accordance with an aspect of this invention.

FIG. 5 is a graph representing particles sizes of aluminum-doped zincoxide obtained during investigations leading to this invention.

FIG. 6 is a graph representing light penetration properties ofaluminum-doped zinc oxides obtained during investigations leading tothis invention.

FIG. 7 is a graph representing light acceptance properties ofaluminum-doped zinc oxides obtained during investigations leading tothis invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is generally applicable to methods and systemssuitable for inducing crystallization within thin films. This inventionis particularly applicable to thin films used in applications including,but not limited to, transparent conducting oxides for transparentelectrodes and display windows, thin film solar cells, andoptoelectronic devices as well as photovoltaic absorbent materials suchas those used in solar cells. While the present invention will bedescribed in relation to thin films, and in particular aluminum-dopedzinc oxide, it is foreseeable that the crystallization process describedhereinafter may be applied to other materials and products.

FIG. 1 schematically represents an exemplary embodiment of the presentinvention wherein a laser system 10 is used for high speed lasercrystallization (HSLC). The system 10 directs a laser beam 14 along anoptical path 30 to impinge upon a thin film 24. The thin film 24 iscovered by an optional confinement layer 26 that is transparent to thelaser beam 14. The system 10 includes a laser 12 that generates thelaser beam 14 and a beam expander 22 that expands the laser beam 14before it impinges on the thin film 24. The system 10 can also includeone or more optical elements, for example mirrors 20, that redirect thelaser beam 14 along the optical path 30 from the laser 12 to the thinfilm 24. The system 10 can also include additional optical elements forfocusing and attenuating the laser beam 14, for example, an aperture 16,a power attenuator 18, and/or a beam shaper 50. Laser beam spot size andshape may be regulated by the aperture 16. After the aperture 16, thepower attenuator 18 comprised of a polarizer and a rotating stage servesto control the delivered laser power. The laser beam expander 22 and alaser beam scanner 34 may be used to achieve high speed processing ofthe thin film 16 (up to 10 m/s). During the process, the laser 12 pulsesto create a localized rapid heating and cooling condition, which isadvantageous for rapid growth of nanoscale crystals into large crystals,as well as for decreasing defects such as grain boundaries. As usedherein, the phrase “rapid heating and cooling” is defined as less thanone microsecond.

FIG. 2 schematically represents an enlarged view of the laser beam 14being directed along a direction 32 while impinging the thin film 24.The thin film 24 is represented in FIG. 2 as including a substrate 42and at least one target layer 36, the latter of which is intended toundergo crystallization. Layers 38 and 40 in FIG. 2 are representativeof additional optional layers that may be deposited if necessary basedon the application of the thin film. For example, the thin film 24 maybe intended for use in solar cells, in which case at least one of thelayers 38 or 40 may be a photovoltaic absorbent layer.

The system 10 may be used with thin films deposited by any suitableprocesses known in the art including, but not limited to, physical vapordeposition (sputtered thin films, pulsed laser deposited thin films,co-evaporated thin film), atomic layer deposition (ALD), chemicalbathing (such as CdS buffer layer), electrochemical deposition, androll-to-roll printing or ink-jet printing (nanoparticles or nanowires).As previously discussed, the resulting thin film comprises one or morelayers deposited on the substrate. At least the target layer 36 isformed of nano-scale particles.

The laser 12 can be a neodymium-doped yttrium aluminum garnet (Nd:YAG)laser which can generate laser beams 14 having wavelengths of, forexample, 1064 nm, 532 nm or 355 nm using methods such as second harmonicgeneration or frequency doubling. The thin film 24 can be placed on anX-Y stage 28 (FIG. 1) adapted to move the thin film 24 as desired. Thelaser 12 is preferably capable of providing rapid short duration pulses(for example, 5 nsec pulses) and/or perform high speed laser scanning ofthe target layer 36, for example 10 m/s, by using the high speed laserbeam scanner 34. The scanning can be performed by movement of the laserbeam 14 or movement of the thin film 24, or both. Multiple pulse effectscan be obtained by spatial overlap between pulses, which is controlledby the beam size, scanning speed and repetition rate.

The target layer 36 absorbs most of the laser energy, thereby creating alocalized high-temperature within the target layer 36 that causes thetarget layer 36 to become more dense and smooth and forms largercrystals through grain growth. The enlarged view of FIG. 2 furtherrepresents the effect of the laser beam 14. On the right side of theenlarged view, the laser beam 14 has not yet impinged the target layer36 and the target layer 36 comprises a plurality of tightly packedcrystals 48 from the deposited particles. In the middle of the enlargedview, the laser beam 14 is impinging the target layer 36 and the targetlayer 36 is becoming densified to have larger crystals 46 with fewergaps. On the left side of the enlarged view, as a result of impingementof the target layer 36 by the laser beam 14, the target layer 36comprises larger crystals 44 with significantly fewer gaps. When thelaser beam 14 passes over the entire target layer 36, the entire targetlayer 36 will have larger crystals similar to the crystals 44 on theleft side of the enlarged view in FIG. 2.

According to preferred aspects of the invention, the laser system 10performs a high speed laser crystallization (HSLC) process capable ofincreasing the size of nanocrystals (i.e., larger than 100 nm) andprocessing selective materials at selective locations without damagingother components. The HSLC process is preferably a rapid approach thatis achieved by delivering multiple laser pulses in rapid succession(e.g., 30 pulses of 5 ns each) to a target. The crystal growth anddensification are completed almost instantaneously after the pulses.HSLC does not require high temperature and can be carried out at roomtemperature. In addition, HSLC can often be performed without the needfor a vacuum. Some materials may require a confinement layer 26 (forexample, glass) over the target layer 36 or an inert gas environment inorder to prevent the thin film 24 from being oxidized. In addition, alow vacuum chamber with evacuation system may be needed for processingmaterials that are toxic. Even so, HSLC processes that can be performedwith the laser system 10 are capable of achieving substantial energy andsetup savings.

Operating parameters of the system 10 are preferably selected tominimize the heating effects on the substrate 42. For this purpose, afinite element analysis (FEA) model can be used to predict the operatingparameters of the system 10 necessary to cause crystallization of thetarget layer 36 of the thin film 24, preferably in an environment atnear room temperature and atmospheric pressure, on the particularsubstrate 42 to be used. An example of such a model is represented inFIG. 3. The model uses first simulates the laser-nanoparticleinteraction based on parameters of the system 10 (laser power, beamradius, scan speed, etc.), optical and electrical properties of thetarget layer 36 (refractive of index, electrical conductivity, etc.),and pre-coated conditions of the target layer 36 (thickness, particlediameter, etc.)(This step is labeled as the EM model in FIG. 3). Themodel then uses the result to simulate the heat conduction from thetarget layer 36 to the substrate 42 as a result of laser heating basedon heat sources, thermal properties of the thin film 24 (thermalconductivity, specific heat capacity, density, etc.), initial conditionsof the thin film 24, and boundary conditions (This step is labeled asthe HT model in FIG. 3). Resistive heating (Q_(RH)), i.e., the outputfrom the first simulation, is coupled to the second simulation as thesecondary heat source which eventually causes temperature elevation.Considering the size effects, calculated size dependent properties ofnanomaterials are used. The laser source, initial conditions andboundary conditions can be properly selected in order to solve the modeland thereby determine optimum operating parameters for the system 10 fora specific substrate 42.

The target layer 36 may be composed of various materials such as, butnot limited to, an aluminum doped zinc oxide, CuInSe₂, CdTe, GaAs,silicon, etc. The substrate 42 may be composed of any material suitablefor thin films, whether the material is rigid or flexible. Due to thelow operating temperature of the HSLC process, the substrate 42 may becomposed of low melting temperature materials such as plastics, polymersand papers. Other suitable materials for the substrate 42 include, butare not limited to, glass and metal foils. FIG. 4 shows scanned imagesof a surface of a representative transparent conducting oxide (TCO)after HSLC was performed on TCOs deposited on various substrates 42.FIG. 4(a) shows a surface after the TCO was deposited by pulsed laserdeposition (PLD) onto a substrate formed of a polyimide filmcommercially available under the name Kapton® (registered by DuPont) andFIG. 4(b) shows the same surface after the HSLC laser performed 15pulses on the TCO at a power level of 25 mJ/cm². FIG. 4(c) shows asurface after the TCO was deposited onto a soda lime glass (SLG)substrate by PLD and FIG. 4(d) shows the same surface after the DLPRlaser performed 30 pulses on the TCO at a power level of 30 mJ/cm². FIG.4(e) shows a surface after the TCO was deposited onto an aluminum foilsubstrate by PLD and FIG. 4(f) shows the same surface after the DLPRlaser performed 100 pulses on the TCO at a power level of 60 mJ/cm². Asevident from FIGS. 4(a)-(f), HSLC was capable to form relatively largecrystals within the target layer 36 on various substrates 42.

In another exemplary investigation, a deposition method in accordancewith an aspect of this invention was carried out at room temperature.Before deposition, soda lime glass sample was cleaned by acetone,methanol, and de-ionized water in an ultrasonic cleaner, sequentially.ZnO (about 99.99% pure) and Al-doped ZnO (about 2% Al and about 98% ZnO)targets were ablated using a KrF excimer laser (wavelength of about 248nm, pulse duration of about 25 ns). The target distance was about 80 mm.The rotation of the target and sample was set to be approximately 7 and5 RPM, respectively. An i-ZnO film (about 50 nm) was deposited with alaser fluence (F) of about 1.5 J/cm² and a repetition rate (R) of about10 Hz for approximately 20 min. An Al-doped ZnO (about 250 nm) film wasdeposited by a laser fluence of about 0.5 J/cm² and a R=5 Hz for about90 min. The i-ZnO and Al-doped Zno films were deposited in an atmospherehaving an oxygen gas pressure of approximately 150 mTorr andapproximately 1 mTorr, respectively. After PLD, the sample was placed ina vacuum chamber at approximately 10 mTorr. The same laser was used forHSLC with R approximately equal to 1 Hz. The laser beam was shaped tosquare top-hat (about 8×8 mm). The sample was placed on a motorizedstage which enabled translations along both X and Y axes.

Further investigations of the HSLC of this invention were conducted onAl-doped ZnO film with laser fluence in ranges of about 20 to 200 mJ/cm²and about 10 to 150 pulses (N). The investigations found that laserfluence (F) as high as 50 mJ/cm² will lead to ablation of Al-doped ZnO.Similar results were observed in investigations on indium tin oxidefilms. Laser fluencies between about 25 and 30 mJ/cm² were foundsuitable for HSLC. However, optimal processing conditions also depend onN. For example, N=50 produces F=25 mJ/cm² and N=30 produces F=30 mJ/cm².Multiphysics electromagnetic-heat transfer (the FEA model) simulationshowed that as a result of laser irradiation, the temperature of theAl-doped ZnO films increased to approximately 1695° K, 1180° K, and 850°K in 50 ns for F=50, 30, and 20 mJ/cm², respectively. These temperaturescorresponded to approximately 103% of T_(B), approximately 85% of T_(m),and approximately 60% of T_(m) of Al-doped ZnO, respectively, whereT_(B) and T_(m) stand for calibrated boiling point and melting point ofAl-doped ZnO, respectively. It is believed that when the temperature ishigher than T_(B), vaporization and then ablation is expected. Thisexplains why the ablation to Al doped ZnO is observed when F=50 mJ/cm².According to the Thornton structure zone model, crystallization isbelieved to occur when the temperature is above 75% of T_(m). As thermalenergy continues, large crystals tend to merge smaller counterpartsuntil they impinge on each other. Simulations predicted that laserfluence of about 30 mJ/cm² satisfies the condition to triggercrystallization while 20 mJ/cm² does not. Both the investigations andsimulations suggested that laser induced rapid melting andsolidification is the driving force for Al doped ZnO crystallization andgrowth and that when F is between about 25 to 30 mJ/cm² the resultingtemperature is higher than 75% of T_(m) and therefore crystallizationwill likely occur. When F is about 20 mJ/cm², the resulting temperatureis less than 60% of T_(m) which will likely not produce crystallization.It is also worth mentioning that the temperature of the SLG substratealways stays below 470° K.

The investigations showed that the deposition rate is approximately 2.5and approximately 2.78 nm/min for i-ZnO and Al doped ZnO, respectively.Al doped ZnO films obtained from PLD displayed a columnar structure withporous structure comprised of tapered crystallites separated by internalvoids. This corresponds to zone 1 of the Thornton Structure Zone modelwhen temperature is 10%-30% of melting point of Al doped ZnO. A majorityof the particles were observed to have a size of about 30 to 70 nm priorto HSLC (d denotes diameter for particles). After HSLC, Al doped ZnOexperienced crystallization and growth which led to a morphologicalchange. Instead of discrete nanoparticles, the surface was comprised offaceted and flat grains with grain boundaries. A histogram of Al dopedZnO particle/crystal size and distribution is represented in FIG. 5,which displays that after HSLC, not only did the Al doped ZnO undergocrystallization but also growth occurred to the nanoparticles. BeforeHSLC, roughly 23% of the particles were between 30 and 40 nm and nonewere above 100 nm; however, after HSLC, none of the crystals were below40 nm (d denotes diagonal length for crystals), and 15% of the crystalswere above 100 nm.

The resistivity of the Al doped ZnO film deposited by PLD was measuredto be approximately 1.40×10-3 Ωcm. After HSLC, the resistivity decreasedin observed samples by a minimum of 2.23×10-4 Ωcm. These results suggestthat when nanosecond pulsed laser irradiation is used, crystallizationand growth of crystals occur as a result of laser induced melting andsolidification and crystallization reorganizes the microstructure of Aldoped ZnO. Growth of Al doped ZnO refers to coalescence of a fewnanocrystals into bigger crystals which decreases internal defects suchas the inter-crystal gaps and grain boundaries.

Hall effect measurement suggested that as a result of HSLC, Hallmobility in the samples increased by two orders, from about 6.56 to morethan 100 cm²/vs, with a maximum of 382.83 cm²/vs. Carrier concentrationdensity was determined to have dropped by two orders from about1.098×10²¹ to minimum of 4.375×10¹⁹ cm⁻³. Starting film homogeneity,testing configurations, and laser fluence fluctuations are believed tobe responsible for these variations among the samples. Thesemeasurements show that Al doped ZnO films processed by HSLC have higherHall mobility and lower carrier concentration than those produced byprior methods known in the art. Increased Hall mobility indicates thatelectrons move with little resistance in the film because HSLC reducesits internal defects and increases grain size. The decrease in carrierconcentration is believed to be due to high zinc vacancies, which areproduced during a lack-oxygen crystallization process wherein a greatamount of excited electrons are captured from the doped Al and thus thedensity of effective electrons is decreased. Lower carrier concentrationleads to film band gap shrinkage (ΔE_(g)), hence widening in solarspectrum acceptance.

The investigations indicated that the acceptance of solar spectrum ofHSLC-processed Al doped ZnO film is about 215 nm broader than that ofthe PLD-deposited Al doped ZnO film. Therefore, this process allows moresunlight to pass through the film which is beneficial in specificapplications, such as thin film solar cells. Both transmittance andabsorbance spectra of Al doped ZnO thin films deposited directly by PLDand three HSLC processing conditions are presented in FIG. 6. FIG. 6shows that after HSLC, an aluminum doped zinc oxide film's transmissionincreased by 9%, 15%, and 16% in UV, visible, and NIR ranges while theoptical absorption decreased significantly.

The band gap of Al doped ZnO films was evaluated using direct band gapmethod by plotting the absorbance squared versus energy andextrapolating to zero. The band gaps were determined to be approximately3.92, 3.88, and 3.71 eV for films deposited by PLD, HSLC (F=30 mJ/cm²,N=30), and HSLC (F=25 mJ/cm², N=50), respectively. Band gap shrinkageswere observed which is believed to correspond with the decrease incarrier concentration density (n). The Burstein and Moss model describesthat band gap shrinkage (ΔE_(g)) correlates to n^(2/3). In this case,measured carrier density of Al doped ZnO films was about 4.375×10¹⁹ cm⁻³after HSLC treatment. Effective mass of electrons and holes of Al dopedZnO are believed to be approximately 2.551×10⁻³¹ kg and approximately5.374×10⁻³¹ kg, respectively. When substituting n with 4.375×10¹⁹ in theBurstein and Moss model, it can be calculated that ΔE_(g) to be about162 meV. According to the measured band gap shrinkage using opticalspectra, band gap shrinkage as large as 210 meV were observed, asrepresented in FIG. 7, which corresponds to a 260 nm expansion ofacceptable sunlight by the film. The discrepancy was expected since then^(2/3) correlation stated in Burstein and Moss model is valid for nless than 4.2×10¹⁹ cm⁻³. When n is slightly greater than 4.2×10¹⁹, asudden decrease in band gap is expected.

The above investigations showed that, under optimal laser processingconditions, it is possible to deposit high mobility (384 cm²/vs) Aldoped ZnO thin film on flexible substrates, metal foils and glass. It isbelieved that this is because the HLSC process removes the crystaldefects such as grain boundaries, inter-crystal gaps, and vacancies.

While the invention has been described in terms of a specificembodiment, it is apparent that other forms could be adopted by oneskilled in the art. For example, the physical configuration of thesystem 10 could differ from that shown, and materials and processesother than those noted could be used for the thin film 16. Therefore,the scope of the invention is to be limited only by the followingclaims.

1. A method of inducing crystallization in thin films with a lasersystem, the method comprising: obtaining a thin film comprising asubstrate and a transparent conducting oxide (TCO) layer deposited onthe substrate, wherein the TCO layer comprises nano-scale particles;determining the heat conduction between the TCO layer and the substrateof the thin film based on thermal input from the laser system toidentify operating parameters for the laser system that causecrystallization and crystal growth of the nano-scale particles of theTCO layer in an environment at near room temperature with the substrateremaining at a temperature below the temperature of the TCO layer;locating a confinement layer over the thin film; transmitting a laserbeam of the laser system along an optical path to impinge the TCO layerof the thin film, wherein the confinement layer is transparent to thelaser beam and the laser beam travels through the confinement layerprior to impinging the TCO layer when transmitting the laser beam alongthe optical path; and then pulsing the laser beam to create a localizedrapid heating and cooling of the TCO layer, wherein the laser system isoperated at the operating parameters identified in the determining stepto crystallize and induce crystal growth of the nano-scale particles ofthe TCO layer and maintain the substrate at a temperature below thetemperature of the TCO layer.
 2. The method of claim 1, wherein the TCOlayer comprises aluminum doped zinc oxide.
 3. The method of claim 1,wherein the TCO layer comprises indium tin oxide.
 4. The method of claim1, wherein the substrate is chosen from the group consisting of glass,metal foils, plastics, polymers, or papers.
 5. The method of claim 1,further comprising expanding the laser beam to enlarge the surfaceregion of the thin film covered by the laser beam using a beam expander.6. The method of claim 1, further comprising scanning the laser beamacross a specific region of the thin film.
 7. The method of claim 1,wherein the laser beam is pulsed such that the TCO layer is heated to atemperature of at least 60 percent of a melting point of the TCO layerand below a boiling point of the TCO layer.
 8. The method of claim 5,wherein obtaining the thin film comprises depositing the TCO layer onthe substrate.
 9. The method of claim 1, wherein the pulsing stepcomprises generating a series of pulses of the laser beam having aduration of approximately 5 nanoseconds each.
 10. The method of claim 1,wherein the substrate is not damaged during the transmitting step andpulsing step.
 11. A system comprising: a thin film comprising asubstrate and at least one transparent conducting oxide (TCO) layer, theTCO layer comprising nano-scale particles therein; a confinement layerover the thin film; and a laser generating a pulsing laser beam along anoptical path to impinge the TCO layer of the thin film and locally andrapidly heat and cool the TCO layer while the substrate is at atemperature below the temperature of the TCO layer such thatcrystallization and crystal grow of the nano-scale particles occurs inthe TCO layer, the confinement layer being transparent to the laser beamand the laser beam traveling through the confinement layer prior toimpinging the TCO layer when the laser generates the pulsed laser beam.12. The system of claim 11, further comprising means for scanning thelaser beam across a specific region of the thin film.
 13. The system ofclaim 11, wherein the laser is configured to pulse the laser beam suchthat the TCO layer is heated to a temperature of at least 60 percent ofa melting point of the TCO layer and below a boiling point of the TCOlayer.
 14. The system of claim 11, wherein the thin film was formed by aprocess comprising depositing the TCO layer on the substrate.
 15. Thesystem of claim 11, further comprising a beam expander adapted toenlarge the surface area of the thin film covered by the laser beam. 16.The system of claim 11, wherein the TCO layer comprises aluminum dopedzinc oxide.
 17. The system of claim 11, wherein the TCO layer comprisesindium tin oxide.
 18. The system of claim 11, wherein the substrate ischosen from the group consisting of glass, metal foils, plastics,polymers, or papers.
 19. The system of claim 11, wherein the laser is aneodymium-doped yttrium aluminum garnet (Nd:YAG) laser.
 20. A method ofinducing crystallization in thin films with the laser system of claim11, the method comprising: obtaining the thin film, wherein the TCOlayer comprises nano-scale particles; determining the heat conductionbetween the TCO layer and the substrate of the thin film based onthermal input from the laser system to identify operating parameters forthe laser system that cause crystallization and crystal growth of thenano-scale particles of the TCO layer in an environment at near roomtemperature with the substrate remaining at a temperature below thetemperature of the TCO layer; transmitting the laser beam of the lasersystem along an optical path to impinge the TCO layer of the thin film;and then pulsing the laser beam to create a localized rapid heating andcooling of the TCO layer, wherein the laser system is operated at theoperating parameters identified in the determining step to crystallizeand induce crystal growth of the nano-scale particles of the TCO layerand maintain the substrate at a temperature below the temperature of theTCO layer.